Formation And Characterization Of Ti-Zr Based Conversion Coatings On Magnesium Alloy

In this paper, the treatment process of Ti-Zr conversion coating on AZ31 B magnesium alloy and the conversion solution formula were studied. With potassium fluorozirconate and potassium fluorotitanate as film formation main salt, adding magnesium sulfate,tannic acid, and sodium fluoride into the conversion solution, using this conversion solution, dense and uniform Ti-Zr conversion coating of magnesium alloy was prepared at room temperature. Ti conversion coating and Zr conversion coating of magnesium alloy were obtained, then studied the effects of parameters on the conversion coating corrosion resistance. On the basis of this research, the orthogonal experiment was used to prepare the Ti-Zr conversion coating., Electricity chemical workstation, energy spectrum（EDS）, X-ray photoelectron spectrometer（XPS）, scanning electron microscope（SEM）, and surface properties measuring instrument were applied to test the characterization of chemical conversion and the surface morphology.The best conversion treatment process parameters of Magnesium alloy Ti-Zr conversion coating: K₂ Ti F₆ 0.75 g/L, K₂ Zr F₆ 1.75 g/L, Mg SO₄ 1.00 g/L, tannin acid 0.05 g/L, Na F 1.5 g/L, treating 10 minutes at room temperature.Ti-Zr conversion coating, Ti conversion coating, Zr conversion coating were prepared on AZ31 B magnesium alloy. After electrochemical workstation test, it showed that the polarization resistance of the conversion coatings had a substantial improvement compared with the blank Mg alloy, and the corrosion current was two orders of magnitude lower.SEM showed that the surface of Ti-Zr, Ti and Zr conversion coatings appeared smooth dry river beds, in which the crack of Zr and Ti salt conversion coatings were wider than Ti-Zr conversion coating, and the ranking were not as neatly as Ti-Zr conversion coating. EDS and XPS test showed that the main elements composition of Ti-Zr conversion coating of magnesium alloy were Ti, Zr, Al, O, C F, Na, Mg, etc., Zr conversion coating of magnesium alloy was mainly composed of element Mg, O, F, Zr, Al, C, Zn and Mn, main elements of Ti conversion coating were Mg, O, F, Al, C, Zn, Ti and Mn. And the films mainly composited by organic complex, metal oxides, metal hydroxide and metal fluorides and so on.Surface properties measuring instrument was used to test the surface roughness, the results indicated that the conversion coating arithmetic average roughness（Ra） was about 0.1μm, reflecting the uniformity of conversion coating was favorable.